In accordance with the present disclosure, this object is solved by a hydraulic system comprising at least two main control valves and a hydraulic pilot control system for actuating the main control systems. According to the present disclosure it is provided that the hydraulic pilot control system and/or the main control valves are constructed such that the at least two main control valves open one after the other. In accordance with the present disclosure it can thus be achieved via the hydraulic or mechanical configuration of the hydraulic system that the main control valves are opened in a certain sequence and thus a cascade connection is realized. In particular, the system can be constructed such that the at least two main control valves open at different control pressures of a common control transmitter. This also allows to realize a cascade connection in a hydraulically piloted multi-circuit system, in which the main control valves open in a certain sequence.
In a first variant, the cascade connection can be realized via mechanically and/or hydraulically differently designed main control valves.
In particular, the at least two main control valves can be equipped with springs of different spring force, so that the main control valves open at different control pressures due to the different spring force. The spring of a first main control valve for example can open in a first control pressure range, whereas the spring of a second main control valve opens in a second control pressure range. Otherwise, the main control valves can be constructed identically.
Alternatively or in addition, the at least two main control valves can include different valve rods and/or valve housings, which lead to an opening of the at least two main control valves at different strokes. In this variant, the opening starts of the main control valves are mechanically fixed differently on the valve rods and the valve housings, respectively. This can be effected for example in the form of grooves or holes on the valve rods.
As a result, a cascade connection can be established by valve hardware without corresponding switching logic. The valves thus open at different strokes and hence at different control pressures.
Furthermore, it can be provided according to the present disclosure that at least one of the main control valves is charged with a counterpressure which counteracts the control pressure. The same effect thereby can be achieved as by an increased spring strength, since the counterpressure adds up to the spring pressure and first must be overcome by the control pressure, in order to lead to an opening of the main control valve. In particular, the counterpressure can be constant. Advantageously, a corresponding pressure source therefore is provided.
Furthermore, the cascade connection also can be implemented by a corresponding design of the pilot control unit. For example, there can also be used identical main control valves.
In particular, it can be provided that at least one of the main control valves is actuated via a pressure reducing valve whose output pressure is actuated via the control pressure for another main control valve. Via the pressure reducing valve, another control pressure thereby can be generated for the one main control valve. In particular, the pressure reducing valve can have a pressure ratio unequal to 1 between control pressure and outlet pressure, so that the outlet pressure for actuating the one main control valve is in a fixed ratio to the control pressure for the other main control valve.
Alternatively or in addition, it can be provided that via a pressure shut-off valve at least one of the main control valves is charged with a counter control pressure which counteracts the control pressure. Advantageously, the pressure shut-off valve is charged with the control pressure, so that the counter control pressure rises with the control pressure up to a shut-off pressure. A later opening start also can be achieved thereby in the main control valve, which is charged with the counter control pressure.
Combinations of the above-described possibilities are of course also conceivable. In particular, a first main control valve can be actuated via a pressure reducing valve, whereas a second main control valve is charged with a counter control pressure via a pressure shut-off valve.
Furthermore, the above-described possibilities can of course also be used in more than two main control valves.
In the variants described first, which employ mechanically and/or hydraulically differently designed main control valves, correspondingly different spring strengths or correspondingly differently machined valve rods or valve housings can be used.
Furthermore, in a cascade connection more than one pressure reducing valve or more than one pressure shut-off valve can be used via the pilot control unit, which then correspondingly operate with different pressure ratios or with different shut-off pressures.
Advantageously, the hydraulic system according to the present disclosure includes a common control transmitter via which the at least two main control valves can be actuated. In particular, this control transmitter can generate a control pressure for actuating the at least two main control valves. Despite the common control transmitter, the design of the main control valves or the pilot control unit according to the present disclosure then provides different opening starts of the main control valves.
In a first embodiment, the hydraulic system according to the present disclosure furthermore includes a common high-pressure supply for supplying the at least two main control valves with hydraulic pressure. Advantageously, the high-pressure supply comprises a variable displacement pump which is actuated by the connected load or loads as required. The cascading of the opening starts according to the present disclosure allows the use of such pressure supply despite a hydraulic pilot control.
According to the present disclosure, the variable displacement pump advantageously is actuated via a load sensing arrangement. In particular, the variable displacement pump is actuated such that a certain pressure drop is maintained over all main control valves and at the same time a maximum pressure is not exceeded. Advantageously, a downstream summation is effected for actuating the load sensing arrangement.
In a second embodiment, the at least two main control valves of the hydraulic system may be separately supplied with hydraulic pressure by at least two separate high-pressure supplies. Advantageously, the high-pressure supplies each comprise a variable displacement pump.
In such an embodiment, if only small flow rates of hydraulic fluid are required, the cascade control of the present invention will only open one of the two main control valves, such that only one of the at least two hydraulic pump will be used to supply the one or more loads with hydraulic pressure. If more hydraulic power is required, the control will also open the second main control valve, such that also the second hydraulic pump is used to supply pressure.
Also in this case, the variable displacement pumps may advantageously be actuated via a load sensing arrangement.
Of course, the system of the present invention can also be used with more than two main control valves and/or more than two hydraulic pumps and/or more than two loads. In this case, the more than two main control vales preferably open in a pre-defined sequence.
In a first embodiment, the at least two main control valves separately control at least two separate loads.
For example, the at least two main control valves may control separate hydraulic cylinders. For example, the at least two hydraulic cylinders may be used to successively move separate elements, such as telescoping in or telescoping out several telescopic elements of a telescopic arm.
Therein, one or several hydraulic pumps may be used for supplying hydraulic pressure, as described above.
In a second embodiment, the at least two main control valves control a common load. This embodiment can in particularly be used if the desired maximum flow rate for controlling this load cannot be achieved by a single main control valve.
In a preferred embodiment, the two main control valves may be separately supplied with hydraulic fluid by separate hydraulic pumps, as described above. Alternatively, the pressure supply may be provided by a common hydraulic pump.
Beside the hydraulic system, the present disclosure furthermore comprises a pilot control system as it has been described above. In particular, it is a pilot control system which hydraulically realizes the cascade connection according to the present disclosure. In particular, as shown above, a pressure reducing valve and/or a pressure shut-off valve can be used for actuating at least one of the main control valves.
Furthermore, the present disclosure comprises a set of at least two main control valves for a hydraulic system as it has been described above. In particular, the main control valves are mechanically and/or hydraulically designed differently. In particular, the two main control valves include springs with different spring force, and/or mechanically differently machined valve rods or valve housings, which lead to an opening start at different strokes.
Advantageously, the pilot control system or the set of at least two main control valves are designed such as has already been set forth above in detail.
The present disclosure furthermore comprises a hydraulically driven implement with a hydraulic system as it has been described above. In particular, the implement is a mobile implement. Particularly, the present disclosure is employed in construction, earth-moving and/or material-handling machines. In particular, the present disclosure comprises a hydraulic excavator with a hydraulic system according to the present disclosure.
In an embodiment, the implement comprises at least two hydraulic pumps for supplying hydraulic pressure for loads of the implement, wherein the at least two main control valves are separately supplied by the at least to hydraulic pumps.
In an embodiment, the at least two main control valves supply the same load with hydraulic fluid.
The load that is supplied by the at least two main control valves may for example be a slewing gear, a traveling gear and/or a hydraulic cylinder for lifting and/or moving a boom or tool.
In a further embodiment, the at least two main control valves separately supply at least two separate loads.
The at least two loads for example can be a slewing gear, a traveling gear and/or a hydraulic cylinder for lifting and/or moving a boom or tool.
The present disclosure will now be explained in detail with reference to exemplary embodiments and drawings.
It should be understood by one skilled in the art that the figures utilize standardized symbols for hydraulic systems, and thus example embodiments may optionally include the detailed features of components as represented.